PHOENIX, May 1 (Reuters) - The top official at a Phoenix veterans hospital was placed on indefinite leave on Thursday while regulators probe whistleblowers' claims that delayed care may have led to the deaths of as many as 40 veterans, the head of U.S. veterans affairs said.

Secretary of Veterans Affairs Eric Shinseki said in a statement that Director Sharon Helman was put on administrative leave "until further notice" pending a "thorough" review by the agency's inspector general's office.

Also put on leave were associate director Lance Robinson and a third individual whose name and position were not disclosed, the Department of Veterans Affairs said.

"It is important to allow an independent, objective review to proceed," Shinseki said. "These allegations, if true, are absolutely unacceptable and if the inspector general's investigation substantiates these claims, swift and appropriate action will be taken."

Helman and Robinson could not be reached for comment.

Allegations into problems at the busy central Phoenix hospital have surfaced in recent weeks, with claims that as many as 40 veterans may have died while waiting for medical appointments at the facility.

The Arizona Republic, which has investigated complaints of delayed care at the Phoenix VA Health Care System, reported earlier this month that U.S. Representative Jeff Miller, chairman of the House Committee on Veterans Affairs, had disclosed at a committee meeting that up to 40 veterans might have died due to delayed care at the busy facility.

Miller has asked the Department of Veterans Affairs to issue a preservation order to safeguard all documents at the Phoenix facility to allow his committee and the VA inspector general to fully investigate the matter.

Whistleblowers, including retired physician Sam Foote, also allege there was a secret list kept to mask the delayed care.

"The scheme was deliberately put in place to avoid the VA's own internal rules," Foote told CNN this week. "They developed the secret waiting list."

Shinseki said he takes the allegations very seriously. He gave no timetable for when the investigation would be completed.

Three Arizona congressmen this week called for Helman and top hospital administrators to resign in the face of the allegations. The state's two U.S. senators also have been vocal about potential problems at the facility.

Arizona Senator John McCain, a military veteran and the state's senior senator, said in a message on Twitter that the hospital's move was "appropriate." (Editing by Alex Dobuzinskis; Editing by Richard Chang and Ken Wills)